Units of Radiation Measurements, Quality Specification, Half-Value Thickness, Filters, and Filtration.pptx

Units of Radiation Measurements, Quality
Specification, Half-Value Thickness, Filters, and
Filtration
Presenter: Dheeraj Kumar
MRIT, Ph.D. (Radiology and Imaging)
Assistant Professor
Medical Radiology and Imaging Technology
School of Health Sciences, CSJM University, Kanpur

Basics of Radiation Measurements
Radiation measurements are essential for quantifying radiation
exposure, absorbed dose, and activity, providing crucial information for
medical physics and radiology. Let's delve deeper into the units and
their significance:
Units of Radiation Measurements, Quality Specification, Half-
Value Thickness, Filters, and Filtration By-Dr. Dheeraj Kumar
2

Gray (Gy)
• Definition: One gray is equivalent to the absorption of one joule of
radiation energy per kilogram of matter.
• Example: If a tissue absorbs 2 joules of radiation energy per kilogram,
the absorbed dose would be 2 Gy.
3

Sievert (Sv)
• Definition: Sievert is a unit used to measure the biological effects of
ionizing radiation on human tissue.
• Conversion: 1 Sv = 100 rem (roentgen equivalent in man).
• Example: If an individual receives a dose of 0.1 Sv, it implies a
significant risk of developing radiation-induced cancer.
4

Exposure Unit (Roentgen)
• The Roentgen (R) is a unit of measurement for ionizing radiation exposure, particularly in air. It quantifies the
amount of ionization produced by X-rays or gamma rays in a specific volume of air. The Roentgen is crucial
in radiation dosimetry and radiological safety. Let’s discuss into the theory of the Roentgen unit along with
examples:
Definition of Roentgen (R):
• The Roentgen is defined as the amount of X-ray or gamma radiation that produces one electrostatic unit of
charge (either positive or negative) per cubic centimeter of air under standard conditions of temperature and
pressure.
• The symbol for the Roentgen unit is "R."
5

Measurement of Radiation Exposure
Radiation exposure is measured by instruments called ionization chambers, which detect the ionization of air
molecules caused by incoming X-rays or gamma rays.
When radiation interacts with air molecules, it liberates electrons, resulting in ion pairs (positive ions and free
electrons).
The ionization chamber measures the total charge produced by these ion pairs, which is directly proportional to
the radiation exposure.
Calculation and Examples:
• One Roentgen (R) is equivalent to the generation of 2.58 × 10^−4 coulombs of charge per kilogram of air.
• For example, if a certain X-ray beam produces an exposure of 100 R, it means that the radiation has caused the
liberation of 2.58 × 10^−4 coulombs of charge per kilogram of air.
6

4. Applications
The Roentgen unit is commonly used in various applications, including:
• Diagnostic radiology: To measure the intensity of X-ray beams used in
medical imaging procedures such as radiography and fluoroscopy.
• Radiation safety: To assess occupational and environmental exposure to
ionizing radiation and ensure compliance with safety regulations.
• Radiation therapy: To monitor and control the dose of radiation delivered to
cancerous tissues during radiotherapy treatments.
7

Becquerel (Bq)
• The SI unit of radioactivity is the becquerel (Bq), named after Henri
Becquerel, the physicist who discovered radioactivity. The becquerel
is defined as one disintegration or radioactive decay event per second.
It quantifies the activity of a radioactive substance, representing the
rate at which its unstable atomic nuclei undergo radioactive decay.
8

Measurement of Radioactivity
1 becquerel (Bq) = 1 disintegration/second
• Radioactivity is typically measured using specialized instruments such as Geiger-
Muller counters, scintillation detectors, or proportional counters.
• These instruments detect the ionizing radiation emitted by radioactive decay and
convert it into electrical signals or light pulses.
• The number of disintegrations detected per unit time provides the activity of the
radioactive substance in becquerels.
9

Applications of the Becquerel Unit
1. Nuclear Medicine:
1. In medical imaging and therapy, radioisotopes are used as tracers or therapeutic agents.
2. The activity of radiopharmaceuticals is measured in becquerels to ensure the proper dosage for diagnostic or therapeutic
procedures.
2. Environmental Monitoring:
1. In environmental science, the concentration of radioactive isotopes in air, water, soil, and food samples is measured to assess
radioactive contamination.
2. Monitoring stations use becquerels to quantify the levels of radioactivity in the environment and to ensure public safety.
3. Industrial Applications:
1. In nuclear power generation, industrial processes, and non-destructive testing, radioisotopes are used for various applications.
2. The activity of radioactive materials in industrial processes is measured in becquerels to ensure safety and regulatory
compliance.
10

REM
The REM (Roentgen Equivalent Man) is a unit of dose equivalent, used to quantify the biological effect of
ionizing radiation on human tissue. It takes into account both the absorbed dose of radiation and the relative
biological effectiveness (RBE) of the type of radiation. The REM unit is crucial in radiation protection,
occupational safety, and assessing the health risks associated with exposure to ionizing radiation.
• Definition of REM:
• The REM unit represents the dose equivalent in terms of the biological effect of ionizing radiation on human
tissue.
• It is defined as the product of the absorbed dose (measured in gray or rad) and a quality factor (dimensionless),
which accounts for the type of radiation and its relative biological effectiveness.
• 1 REM is equivalent to 0.01 sievert (Sv).
11

Calculation of REM
The formula to calculate REM is:
REM=Absorbed Dose (in rad or Gy)×Quality Factor (dimensionless)
• The quality factor depends on the type of radiation and ranges from 1 for low linear energy transfer (LET) radiation (such as X-rays
and gamma rays) to higher values for higher LET radiation (such as alpha particles and neutrons).
Examples of Quality Factors:
• X-rays, gamma rays, and beta particles: Quality factor = 1
• Alpha particles: Quality factor = 20
• Neutrons: Quality factor varies depending on energy and circumstances, ranging from 2 to 20 or higher
12

Applications of REM
1. Radiation Protection:
1. The REM unit is used in radiation protection guidelines and regulations to establish dose limits for occupational exposure to ionizing radiation.
2. Occupational dose limits are typically expressed in units of millirem (mrem) or REM.
2. Medical Dosimetry:
1. In medical radiation therapy, the REM unit is used to assess the potential biological effects of therapeutic doses of ionizing radiation on healthy
tissues and organs surrounding the targeted tumor.
3. Risk Assessment:
1. The REM unit plays a crucial role in assessing the health risks associated with radiation exposure and determining the appropriate safety measures
and protective actions to mitigate those risks.
1 REM = 0.01 Sv (sievert)
1 millirem (mrem) = 0.001 REM
13

Example
A radiation source emits radiation with an intensity of 10 mGy per hour at a distance of 1 meter. Calculate the absorbed dose at this distance.
Solution:
• The absorbed dose (D) can be calculated using the formula:
D= Intensity × Time
Given:
Intensity = 10 mGy/hour, Time = 1 hour
• Substitute the values into the formula:
D= 10mGy/hour × 1hour =10mGy
Therefore, the absorbed dose at a distance of 1 meter is 10 milligray.
14

Quality Specification in Radiology
• Quality specification in radiology encompasses various parameters
that ensure optimal performance and safety.
15

Image Resolution
• Definition: Image resolution refers to
the clarity or sharpness of an image,
determined by the number of pixels or
lines per unit length.
• Example: In digital radiography, a
higher resolution image allows for
better visualization of fine anatomical
structures, aiding in accurate diagnosis.
16

Image Contrast
• Definition: Image contrast is the difference
in brightness or density between adjacent
areas on an image.
• Example: Contrast is crucial in
distinguishing between different tissues or
pathological conditions. For instance, in
mammography, a high contrast image
helps detect subtle abnormalities in breast
tissue.
17

Image Noise
• Definition: Image noise refers to random
fluctuations in pixel values, resulting in a
grainy or speckled appearance.
• Example: Noise reduction techniques are
essential in computed tomography (CT) to
improve image quality. High noise levels
can obscure important details and
compromise diagnostic accuracy.
18

Dose Optimization
Definition: Dose optimization aims to
minimize radiation exposure to patients while
maintaining diagnostic image quality.
Example: Utilizing dose-reduction techniques
such as automatic exposure control (AEC) in
radiography ensures that patients receive the
lowest possible dose without compromising
image quality.
19

Compliance with Standards
Definition: Compliance with regulatory standards such as IEC 61223-3-
5 ensures adherence to specific quality assurance protocols.
Example: Regular quality control checks, calibration of equipment, and
documentation of procedures are essential for compliance with
standards, guaranteeing consistent and safe radiological practices.
20

Half-Value Thickness (HVT)
Half-Value Thickness (HVT) is a fundamental
concept in radiation physics, particularly in
shielding design and radiation protection. Let's
delve deeper into HVT with numerical examples:
Definition:
1. HVT is the thickness of a material required to reduce
the intensity of a radiation beam by half.
2. It varies with the type and energy of radiation and the
material through which it passes.
21

1. Radiation Attenuation:
When a radiation beam passes through a material, it interacts with the atoms in the material,
resulting in attenuation or reduction in its intensity.
• Attenuation can occur through processes such as absorption, scattering, and transmission.
2. Half-Value Thickness (HVT):
HVT is defined as the thickness of a material that reduces the intensity of a radiation beam
to half of its original value.
• It serves as a measure of the effectiveness of a shielding material in attenuating radiation.
22

23

3. Factors Affecting HVT
The HVT of a material depends on several factors, including:
• Type of radiation: Different types of radiation (e.g., gamma, X-ray, neutron) have
varying penetration depths and require different thicknesses of shielding material.
• Energy of radiation: Higher energy radiation typically requires thicker shielding for
attenuation.
• Atomic number (Z) and density of the material: Materials with higher atomic
numbers and densities are more effective in attenuating radiation and may have
smaller HVT values.
24

4. Applications and Examples
Medical Radiology: - In diagnostic radiology, lead aprons are
commonly used to shield patients from scattered radiation during X-ray
procedures.
Example: The HVT of lead for diagnostic X-rays may range from a few
millimeters to several centimeters, depending on the energy of the X-
rays and the required level of attenuation.
25

Industrial Radiography: - In industrial radiography, lead or concrete
shielding is used to protect workers from exposure to radiation during
non-destructive testing.
Example: The HVT of concrete for gamma radiation used in industrial
radiography may be several centimeters, ensuring adequate protection
for workers in the vicinity.
26

Nuclear Engineering: - In nuclear power plants, shielding materials
such as steel and concrete are employed to minimize radiation exposure
to personnel and the surrounding environment.
Example: The HVT of steel for neutron radiation in nuclear reactors
may be significant, requiring thick shielding to prevent radiation
leakage.
27

5. Measurement and Calculation
• HVT can be determined experimentally by measuring the intensity of
radiation before and after passing through various thicknesses of
shielding material.
• Calculation of HVT involves logarithmic functions and is based on the
relationship between intensity and thickness of the shielding material.
28

Example
Initial intensity of a gamma radiation beam: I0=100 mR/hourI0=100mR/hour, HVT of lead for this radiation:
HVT Lead = 0.5 cm HVT Lead = 0.5cm
The formula to calculate the intensity after passing through a thickness of material is given by:
I=I0×0.5n
Where:
I = Final intensity after passing through thickness
n = Number of HVTs of the material
In this case, we want to find the intensity after passing through 1 cm of lead (which is twice the HVT):
n =
Thickness of lead
𝐻𝑉𝑇 𝐿𝑒𝑎𝑑
=
1𝐶𝑚
0.5 𝑐𝑚
= 2 cm
Substitute n = 2 into the formula:
I =100mR/hour × 0.52 =100mR/hour×0.25 = 25mR/hour
Interpretation:
This means that after passing through 1 cm of lead, the intensity of the gamma radiation beam reduces to 25 mR/hour.
Such calculations are vital for designing effective radiation shielding in medical facilities, ensuring the safety of patients
and staff.
29

Filters in Radiology
Filters play a crucial role in radiology by
modifying the quality and energy
spectrum of X-ray beams. Their function
and selection is essential for achieving
optimal image quality while minimizing
patient dose. Let's explore this topic in
detail, including common filter materials
and their effects on the X-ray spectrum:
30

Purpose of Filters
• Filters are employed in radiology to alter the energy distribution of X-
ray beams, thereby optimizing image quality and reducing patient
dose.
• By selectively filtering out low-energy photons, filters help enhance
image contrast and reduce scattered radiation, resulting in clearer
diagnostic images.
31

Common Filter Materials
• Aluminum (Al): Aluminum filters are commonly used in X-ray equipment for general
radiography. They effectively remove low-energy photons from the X-ray beam, improving image
quality and reducing patient dose.
• Copper (Cu): Copper filters are utilized in mammography to enhance the visualization of breast
tissue. They selectively attenuate low-energy X-rays, allowing for better contrast and detection of
subtle abnormalities.
• Molybdenum (Mo): Molybdenum filters are specifically designed for mammography applications.
They help optimize the energy spectrum of X-rays, improving the visibility of microcalcifications
and small lesions in breast tissue.
32

Effects of Filters on X-ray Spectrum
• Filters preferentially absorb lower-energy X-rays, resulting in a "hardening"
of the X-ray spectrum.
• As a result, the average energy of the X-ray beam increases, leading to
greater penetration of tissues and improved contrast resolution.
• Additionally, filters reduce the amount of low-energy radiation reaching the
patient's skin, thereby lowering skin dose and minimizing radiation risks.
33

Importance of Filtration
Filtration is a critical aspect of radiology
that significantly influences image
quality, patient safety, and radiation dose
management. The importance of
filtration is essential for radiographers,
radiologists, and other healthcare
professionals involved in diagnostic
imaging.
34

Enhancement of Image Quality
• Filtration helps improve image quality by selectively attenuating low-
energy photons, which are more likely to be absorbed by the patient's
body tissues and contribute to image noise.
• By removing these low-energy photons, filtration reduces scatter
radiation and enhances image contrast, allowing for better
visualization of anatomical structures and pathological findings.
35

Reduction of Patient Dose
• One of the primary objectives of filtration is to minimize patient radiation dose
while maintaining diagnostic image quality.
• By filtering out low-energy radiation that contributes minimally to image
formation, filtration helps reduce unnecessary radiation exposure to the patient's
skin and underlying tissues.
• This is particularly important in pediatric imaging and for patients undergoing
repeated X-ray examinations, where dose optimization is critical for long-term
radiation safety.
36

Compliance with Regulatory Standards
• Regulatory bodies such as the Food and Drug Administration (FDA) and the International Electrotechnical
Commission (IEC) establish guidelines and standards for filtration requirements in diagnostic X-ray equipment.
• Compliance with these standards ensures that imaging systems meet minimum filtration specifications,
guaranteeing consistent and safe radiation output.
• Regular quality control checks and documentation of filtration parameters are essential components of quality
assurance programs in radiology departments.
• Filtration plays a crucial role in reducing scatter radiation, which can degrade image quality and increase patient
dose.
• By attenuating low-energy photons that contribute to scatter, filters help improve the signal-to-noise ratio in X-ray
images, resulting in clearer and diagnostically relevant images.
37

Types of Filtration
• In radiology, various types of filtration are employed to tailor the
energy spectrum of X-ray beams, optimize image quality, and
minimize patient radiation dose. The different types of filtration and
their applications is essential for radiographers, radiologists, and other
healthcare professionals involved in diagnostic imaging.
38

Inherent Filtration
Definition: Inherent filtration refers to the filtration that
naturally occurs as X-rays pass through the components of
the X-ray tube and the surrounding materials before reaching
the patient.
Components: Inherent filtration includes the glass envelope
of the X-ray tube, the oil surrounding the X-ray tube, and any
additional filtration within the X-ray tube housing.
Purpose: The primary purpose of inherent filtration is to
remove low-energy, soft X-rays generated by the X-ray tube,
thereby ensuring that the X-ray beam has sufficient energy to
penetrate the patient's body and produce diagnostic images.
39

Added Filtration
Definition: Added filtration involves the placement of
additional filters between the X-ray tube and the patient to
further modify the energy spectrum of the X-ray beam.
Materials: Common materials used for added filtration include
aluminum, copper, and rare-earth metals such as gadolinium.
Purpose: Added filtration helps attenuate low-energy X-rays
that are not useful for diagnostic purposes and contribute
primarily to patient dose and image noise. By removing these
low-energy photons, added filtration enhances image quality
and reduces radiation exposure to the patient.
40

Total Filtration
Definition: Total filtration is the sum of inherent filtration
and added filtration.
Calculation: Total filtration is calculated by adding the
filtration contributed by the components of the X-ray tube
(inherent filtration) to the filtration provided by any
additional filters (added filtration).
Significance: Total filtration determines the overall quality
of the X-ray beam in terms of its energy distribution and
penetration characteristics. It is a crucial parameter for
ensuring compliance with regulatory standards and
optimizing radiation safety in diagnostic imaging.
41

Example: Where we have an X-ray machine with inherent filtration of 0.5 mm aluminum equivalent and an additional aluminum
filter of 2.0 mm thickness placed between the X-ray tube and the patient. We want to calculate the total filtration provided by the X-
ray machine.
Inherent Filtration:
Inherent filtration refers to the filtration naturally present within the X-ray tube.
Given inherent filtration: 0.5 mm aluminum equivalent.
Added Filtration:
Added filtration consists of additional filters placed between the X-ray tube and the patient.
Given added filtration: 2.0 mm aluminum.
Total Filtration:
Total filtration = Inherent filtration + Added filtration
= 0.5 mm aluminum equivalent + 2.0 mm aluminum
= 0.5 mm + 2.0 mm
= 2.5 mm aluminum equivalent.
42

Compensating Filtration
Definition: Compensating filtration involves the
use of filters that vary in thickness across the X-
ray beam to compensate for variations in tissue
thickness and density within the patient's body.
Applications: Compensating filters are
commonly used in mammography and dental
radiography to achieve uniform image density
and contrast across the entire image, even in
regions with varying tissue thicknesses.
43

References
1. Bushberg, J. T., Seibert, J. A., Leidholdt Jr, E. M., & Boone, J. M. (2011). The Essential Physics of Medical Imaging. Lippincott
Williams & Wilkins.
2. Rehani, M. M., & Szczykutowicz, T. P. (Eds.). (2012). Radiation Dose Management in the Nuclear Industry: An Integrated
Approach. Springer Science & Business Media.
3. The International Electrotechnical Commission. (2017). IEC 61223-3-5: Medical electrical equipment - Characteristics of digital X-
ray imaging devices - Part 3-5: Determination of the detective quantum efficiency - Detectors used in mammography. IEC.
4. Shrader, J. A., Casarella, W. J., & Ritenour, E. R. (2016). Introduction to Health Physics. CRC Press.
5. Valentin, J. (2007). Radiation and Your Patient: A Guide for Medical Practitioners. International Atomic Energy Agency.
44

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